<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <style>
        body {
        background-color: #f3f3f3;
        }
        .bgc .one {
        background-color: red;
        }
        .bgc .two {
        background-color: #0f0;
        }
        .bgc .three {
        /* 背景透明 */
        background-color: transparent;
        }
        </style>
        <div class="bgc">
        <div class="one">红色背景</div>
        <div class="two">绿色背景</div>
        <div class="three">透明背景</div>
        </div>
</body>
</html>